module fourBA(a,b,c,s,c_out);
input [3:0]a,b;
input c;
output [3:0]s;
output c_out;
wire c1,c2,c3;
assign s[0]=c^a[0]^b[0];
assign  c1= (c && a[0]) || (c && b[0]) || (b[0] && a[0]);
assign s[1]=c1^a[1]^b[1];
assign  c2= (c1 && a[1]) || (c1 && b[1]) || (b[1] && a[1]);
assign s[2]=c2^a[2]^b[2];
assign  c3= (c2 && a[2]) || (c2 && b[2]) || (b[2] && a[2]);
assign s[3]=c3^a[3]^b[3];
assign  c_out= (c3 && a[3]) || (c3 && b[3]) || (b[3] && a[3]);
endmodule